In the semiconductor art, many schemes are known for interconnecting the various regions of a semiconductor device. These regions include those having P type conductivity and also those having N type conductivity. Generally, it has been quite simple to interconnect semiconductor regions of the same conductivity type, as for example by using a doped polycrystalline material comprised of the same semiconductor as is used to make the device itself. For example, in the case of a silicon semiconductor device having a plurality of N type regions which must be interconnected, a common interconnection is the use of N doped polysilicon. Another interconnect material which has been used is a metal silicide, such as PtSi, which is known as an ohmic contact to P and N semiconductor regions, and as an interconnect material between regions of the same conductivity type. In the semiconductor art, the problem of making electrical interconnections between regions having opposite conductivity type has been a difficult one. Typically, metal lines are used to provide ohmic electrical interconnections between semiconductor regions of opposite conductivity types. However, the use of such metal interconnections reduces the density of arrays of such devices and leads to larger capacitances due to the large area required for each device cell. As an example, a static memory cell comprising bipolar transistors requires that electrical interconnections be made between N and P type regions of the circuit. In the past, these interconnections have been made by overlying metal lines, and the circuits could not be made small and fast.
In the prior art, metal silicides have been suggested as an interconnection material between semiconductor regions of the same conductivity type, and such metal silicides also have generally been used with polysilicon layers in order to reduce the resistance of the polysilicon layer. However, polysilicon has not been used or suggested for use in circuits utilizing bipolar devices where interconnections have to be made between regions of the opposite conductivity type. Thus, prior to the present invention, static memory arrays of bipolar transistors have not been produced which have sufficient commercial advantage to be competitive with other types of static memory cells.
In the practice of the present invention, a technique has been discovered for making interconnections between opposite conductivity regions in a manner which provides good ohmic electrical interconnections and which eliminates the need for some of the metal interconnect lines. This has provided arrays of static memory cells using bipolar transistors which are very dense.
Accordingly, it is a primary object of the present invention to provide a new technique for ohmically interconnecting opposite conductivity type regions in a semiconductor device circuit.
It is another object of the present invention to provide an ohmic interconnection between opposite conductivity types of semiconductor material, in order to provide more dense arrays of semiconductor circuits.
It is another object of the present invention to provide semiconductor circuits in which some metal interconnection lines are eliminated in order to reduce the cell size of devices in the circuit.
It is another object of the present invention to provide ohmic interconnection layers which can be defined with better resolution, for the same lithographic technique, than metal interconnection lines.
It is another object of the present invention to provide a technique for making semiconductor circuits requiring a minimum number of processing steps, in which oxide insulation layers are easily provided without adversely affecting electrical interconnection lines.
It is yet another object of the present invention to provide a static memory cell using bipolar transistors having reduced cell size.
It is another object of the present invention to provide semiconductor circuitry in which metal interconnection lines are eliminated and in which cell size is reduced, in order to reduce the capacitances within said circuit, and in which the electrical properties of the circuit can be improved.
It is a further object of the present invention to provide a technique for interconnecting opposite conductivity regions of a semiconductor material without the need for metal interconnection lines, in a manner to provide semiconductor circuits having enhanced performance characteristics.